1. Field of the Invention
The present invention relates generally to a system used to re-inject drilling cuttings or drilling slurry into an annulus in a subsea well. The present invention provides a system for a providing an increased re-injection rate into a pressure containing conduit while minimizing erosion caused by the flow of the re-injected drill cuttings. The present invention discloses configuring the re-injection inlet into a pressure containing conduit such that a cyclone effect is produced in the flow path of the drill cuttings, which minimizes erosion and may eliminate the need to hard face components of the system.
2. Description of the Related Art
Environmental concerns can be an important issue in the drilling of subsea wells in different regions of the world. In particular, one environmental concern is the storage and safe disposal of cuttings produced during the drilling of subsea wells. Some regions with high particularly high environmental standards are the artic sector and the Norwegian sector of the North Sea. Regulatory requirements have been introduced in the Norwegian sector that would allow for the re-injection of drilling cuttings into the formation while the well is still being drilled.
When drilling a subsea well, drilling mud is used to bring the drill cuttings to the surface where the mixture of drilling mud and cuttings, or slurry, may be filtered and stored. After being filtered, the slurry must be stored or disposed in accordance with environmental regulations of the region. As discussed above, one acceptable form of storage is the re-injection of the slurry into the well formation. The re-injection of slurry can be a complex process and can greatly increase the drilling time, and thus increase the cost spent on drilling a well.
When re-injecting slurry into the well formation for storage the re-injection flow rate may be increased in an attempt to reduce the time that a drilling vessel needs to remain at a well. On disadvantage to increasing the re-injection flow rate is the increase in erosion of components used in the re-injection system. Slurry is a rather abrasive mixture as it contains drillings as well as potentially containing pieces broken off the drilling bit. Increased erosion decreases the useable life of a re-injection system and potentially could lead to failure during use. Although it is desirable to increase the re-injection flow rate, it must be balanced with the erosion caused by the re-injected slurry.
The re-injection of slurry into a well formation may also lengthen the overall drilling time if the well cannot be drilled simultaneous to the re-injection of the slurry. In this instance the re-injection of slurry may be too costly to the overall drilling of a well. The modification of an existing wellhead to enable the use of a re-injection system may also increase the drilling costs per well. The re-injection system may also require a special running tool to install the system onto a subsea wellhead. The special running tool would also be an additional cost to a drilling company as well as the additional time and cost to train personal to use the special running tool. For these reasons, drilling companies may not be interested in using a re-injection system.
The re-injection of slurry into an annulus of the well formation may cause undue wear on well components. For example, the slurry may be injected in an annulus that is between an inner casing and injection mandrel with the slurry being injected from the mandrel side towards the casing. The opening in the injection mandrel may cause the slurry to flow directly at the inner casing potentially causing erosion the inner casing. This possibility of erosion requires hard facing of the inner casing in an attempt to prevent undesirable erosion and possibly failure caused by the flow of the slurry. Hard facing of the casing is expensive and adds to the overall drilling costs associated with the well.
During the drilling stage, the primary function of the well formation is to allow the drilling of the well to begin the production of hydrocarbons. A re-injection system that also utilizes the well formation to store drill cuttings may interfere with the drilling process causing the operators to switch between the two functions. Doing so would lengthen the time required to drill the well, thus increasing the overall drilling costs. To minimize costs, it would be beneficial if the re-injection system allowed for the injection of cuttings for storage while the well was being drilled. One possible problem is the transfer of drilling mud to the drilling site. The mud may have to travel through the re-injection system. It would be beneficial if a re-injection system allowed for the re-injection of slurry into the well while allowing for the passage of drilling mud downhole.
In light of the foregoing, it would be desirable to provide a re-injection system that is adapted to store drill cuttings and/or slurry in an annulus of the well formation. It would further be desirable that the re-injection system may be connected to existing well head designs. It would also be desirable to provide a re-injection apparatus that provides for an increased diameter flow path thus allowing an increased flow of slurry, but also an apparatus that is configured such that the flow of slurry causes minimal erosion to the components of the apparatus. Additionally, it would be desirable to provide an injection system that has balanced injection ports that minimize the erosion on the boundary elements of the storage annulus. It would also be desirable to provide a re-injection system that may allow the drilling of the well concurrent to the injection of slurry within the well formation. Further, it would be desirable for the system to allow for the flow of material, such as drilling mud or cement, through the injection system to downhole locations without interrupting the re-injection of the slurry.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.